1. Field of the Invention
This invention relates to gap/edge bead detection systems. Such structures of this type, generally, employ the use of fiber optic sensor assemblies positioned at the edges of the web and/or between gaps in the sheets in order to detect the absence of material.
2. Description of the Related Art
Extrusion coating is a process where a moving paper web is coated with a molten polymer layer. The polymer layer usually extends beyond the paper web, thereby creating a xe2x80x9cpolymer edge beadxe2x80x9d. It is important that the polymer bead be present to insure that the entire web has been coated. Some polymers are difficult to control at the extrusion extremities of the paper web and/or sheet. These polymers are subject to occasional and unpredictable xe2x80x9cwicking inxe2x80x9d, i.e., the edge of the polymer layer moves inside the edge of the paper web. This xe2x80x9cwicking inxe2x80x9d can be as much as several inches and may continue for just a few seconds or sometimes until corrective action is taken by the operator. Also, the absence of polymer along the entire web is a serious quality defect that can be catastrophic for the customer""s product.
It is known to employ detection systems that use cameras to monitor the web. However, these are very expensive and highly sensitive. Also, these systems often require the web to be shielded from the surroundings.
It is also known to employ photo sensors to inspect a material edge and control process conditions within tolerances required by production. Exemplary of such prior art is U.S. Pat. No. 4,357,899 (""899) to Jones et al., entitled xe2x80x9cCoating Apparatusxe2x80x9d. The major focus of the ""899 reference is in controlling a liquid coating process through reservoir design tanks. However, the inspection system of the ""899 reference cannot be employed on both a sheeting machine where it senses the gap between sheets and on an extrusion coating line where it senses the presence or absence of a polymer coating at the edge of a continuous sheet.
Therefore, it is apparent from the above that there exists a need in the art for a highly accurate and economically reliable gap and edge bead detection for a variety of extruded coatings. The detection system should function without regard to material characteristics such as color, temperature, thickness or chemical make-up. The chemical system should also be unaffected by the physical surroundings. It is a purpose of this invention to fulfill this and other needs in the art in a manner more apparent to the skilled artisan once given the following disclosure.
Generally speaking, this invention fulfills. these needs by providing an edge bead detection system, comprising a frame means, a length of material having a coating located over a portion of the length of material, a slidable mounting means operatively connected to the frame means, an edge bead detection means operatively connected to the mounting means and located a predetermined distance away from the length of material, and a retaining means operatively connected to the mounting means.
In another further preferred embodiment, the detection system is capable of sensing the gap between sheets and the presence or absence of polymer coating along the edge of a continuous sheet without regard to material characteristics such a color, temperature, thickness or chemical make-up. Also, the detection system is unaffected by the physical surroundings.
The preferred system, according to this invention, offers the following advantages: lightness in weight; ease of assembly and repair; good stability; good durability; excellent economy; excellent detection characteristics; excellent sensing characteristics; mobility of location and relocation; physical protection; and ability to realign. In fact, in many of the preferred embodiments, these factors of detection, sensing, mobility of location and relocation, physical protection, and ability to realign are optimized to the extent that is considerably higher than heretofore achieved in prior, known detection systems.